March 2, 2012
09:00 AM (EST)

News Release Number: STScI-2012-10

Dark Matter Core Defies Explanation in Hubble Image

March 2, 2012: Astronomers observed what appeared to be a clump of dark matter left behind
during a bizarre wreck between massive clusters of galaxies. The dark matter
collected into a "dark core" containing far fewer galaxies than would be expected if
the dark matter and galaxies hung together. Most of the galaxies apparently have
sailed far away from the collision. This result could present a challenge to basic
theories of dark matter, which predict that galaxies should be anchored to the
invisible substance, even during the shock of a collision.

The initial observations, made in 2007, were so unusual that astronomers shrugged
them off as unreal, due to poor data. However, new results obtained in 2008 from NASA's Hubble
Space Telescope confirm that dark matter and galaxies parted ways in the gigantic
merging galaxy cluster called Abell 520, located 2.4 billion light-years away. Now,
astronomers are left with the challenge of trying to explain dark matter's seemingly
oddball behavior in this cluster.